This invention relates generally to the usage of ring laser gyroscopes in the determination of azimuth information in a borehole or well. More particularly, it relates to the optimum design and methods of usage of a ring laser gyroscope in the azimuth determination application, in ways to obtain the best possible accuracy along with minimum cost.
The use of one or more angular rate sensors along with one or more suitable acceleration sensors in borehole azimuth determination is well know. U.S. Pat. No. 3,753,296 describes the use of a single angular rate sensor, and U.S. Pat. No. 4,199,869 describes the use of two angular rate sensors, each having two axes of measurement sensitivity. In each of these patents, suitable acceleration sensors are provided to complete the required sensing functions. U.S. Pat. No. 4,197,654 describes the use of a single angular rate sensor having its axis of sensitivity canted so that a component of the input axis of sensitivity lies along the borehole axis.
The environmental and physical limitations of borehole surveying or direction measurement create significant problems for high accuracy measurements using conventional gyroscopes or other conventional angular rate sensors. Wide temperature ranges, acceleration sensitive gyroscope errors, and often severe vibration inputs react to cause measurement errors. The ring laser gyroscope has been shown to approach theoretically ideal gyroscope performance with very accurate rate measuring scale factor, very low temperature and acceleration sensitive errors in gyroscope output, extremely rugged construction, and random errors limited only by the quantum limits of the gyroscopes laser action. These attributes make a ring laser gyroscope highly desirable and attractive for use in the borehole surveying problem.